1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a so-called lateral electric field type liquid crystal display device.
2. Description of the Related Art
In a so-called lateral electric field type liquid crystal display device, on each pixel region on a liquid-crystal-side surface of one substrate out of respective substrates which are arranged to face each other in on opposed manner by way of liquid crystal, a pixel electrode and a counter electrode which generates an electric field between the pixel electrode and the counter electrode are formed, and the light transmittance of the liquid crystal is controlled by components of the electric field substantially parallel to the substrates.
In such a liquid crystal display device adapted to an active matrix type, on the liquid-crystal-side surface of the above-mentioned one substrate, regions which are surrounded by gate signal lines which are extended in the x direction and are arranged in parallel in the y direction and the drain signal lines which are extended in the y direction and are arranged in parallel in the x direction are formed as pixel regions, and a switching element which is operated in response to scanning signals from the gate line, a pixel electrode to which video signals are supplied from the drain signal lines through the switching element and a counter electrode which is arranged in a spaced-apart manner from the pixel electrode are formed on each pixel region.
Then, in performing the color display, there has been known a liquid crystal display device having the structure in which color filters are formed on the above-mentioned one substrate side and the color filters are not formed on the other substrate side. Such a structure is devised to reduce the influence of the displacement of alignment of the other substrate to one substrate to cope with the recent demand for high definition.
However, in the liquid crystal display device having such a constitution, the layer thickness is not made uniform over all color filters of red (R), green (G) and blue (B).
Such a situation occurs when the layer thickness of respective color filters are intentionally set to different values to attain the balance of transmittance or color purity among respective color filters of R, G and B or when the layer thickness is not made uniform over all color filters of red (R), green (G) and blue (B) due to the irregularities in manufacturing the color filters.
In these cases, when the pixel electrodes and the counter electrodes are formed by way of an interlayer insulation film on upper layers of the color filters, the height of the interlayer insulation film with respect to a surface of one substrate is reflected on the layer thickness of the color filters so that the respective heights of the pixel electrodes or the counter electrodes (heights from the surface of one substrate) differ.
This makes the layer thickness of the liquid crystal at respective pixels non-uniform so that the equal light transmittance cannot be obtained with respect to the respective color pixels.
Further, when the interlayer insulation film which is interposed between the pixel electrodes and the counter electrodes is made of resin material or the like which is formed by coating, the thickness of the interlayer insulation film differs depending on the respective pixels of different colors. Accordingly, the voltage drop which differs depending on the interlayer insulation film between the pixel electrodes and the counter electrodes displaces brightness-voltage characteristics thus leading to the collapsing of the color balance of the intermediate gray scale.
The present invention has been made in view of these circumstances and it is an object of the present invention to provide a liquid crystal display device which can enhance the display quality.
To briefly explain the summary of the typical inventions among the inventions disclosed in this specification, they are as follows.
Means 1.
A liquid crystal display device according to the present invention is, for example, characterized in that:
a pair of electrodes which constitute an upper layer and a lower layer with respect to an interlayer insulation film are formed as different layers at respective pixel regions on a liquid-crystal-side surface of one substrate out of respective substrates which are arranged to face each other in an opposed manner by way of liquid crystal,
at two pixel regions which are selected from the respective pixel regions, the heights of background layers on which the electrodes which constitute the lower layers with respect to the interlayer insulation films differ with respect to a surface of one substrate, and
the film thickness of the interlayer insulation film is set small with respect to the high background layer out of the respective background layers which differ in height and is set large with respect to the low background layer out of the respective background layers.
Means 2.
A liquid crystal display device according to the present invention is, for example, characterized in that:
a pair of electrodes which constitute an upper layer and a lower layer with respect to an interlayer insulation film are formed on at least color filters as different layers at respective pixel regions on a liquid-crystal-side surface of one substrate out of respective substrates which are arranged to face each other in an opposed manner by way of liquid crystal from the one substrate side,
at two pixel regions which are selected from the respective pixel regions and on which two color filters of different colors are formed, the heights of surfaces of the color filters differ with respect to a surface of one substrate, and
the film thickness of the interlayer insulation film is set to satisfy a following formula (1).
0 less than film thickness difference of the interlayer insulation film between pixel regions less than film thickness difference of the color filters between pixel regionsxe2x80x83xe2x80x83(1) 
Means 3.
A liquid crystal display device according to the present invention is, for example, characterized in that:
a pair of electrodes which constitute an upper layer and a lower layer with respect to an interlayer insulation film are formed on at least color filters as different layers at respective pixel regions on a liquid-crystal-side surface of one substrate out of respective substrates which are arranged to face each other in an opposed manner by way of liquid crystal from the one substrate side,
at two pixel regions which are selected from the respective pixel regions and on which two color filters of different colors are formed, the heights of surfaces of the color filters differ with respect to a surface of one substrate, and
the film thickness of the interlayer insulation film is set to satisfy a following formula (2).
xc2xcxc3x97film thickness difference of color filter between pixel regions less than film thickness difference of interlayer insulation film between pixel regions,  less than xc2xexc3x97film thickness difference of color filter between pixel regionsxe2x80x83xe2x80x83(2) 
Means 4.
A liquid crystal display device according to the present invention is, for example, based on the constitution of the means 2 or 3, characterized in that the film thickness of the interlayer insulation film is set to satisfy a following formula (3).
film thickness of interlayer insulation film less than {fraction (3/2)} times film thickness of thickest color filterxe2x80x83xe2x80x83(3) 
Means 5.
A liquid crystal display device according to the present invention is, for example, based on the constitution of the means 2 or 3, characterized in that the film thickness of the interlayer insulation film is set to satisfy a following formula (4).
xc2xc times film thickness of thinnest color filter less than film thickness of interlayer insulation film less than {fraction (3/2)} times film thickness of thickest color filterxe2x80x83xe2x80x83(4) 
Means 6.
A liquid crystal display device according to the present invention is, for example, characterized in that:
a pair of electrodes which constitute an upper layer and a lower layer with respect to an interlayer insulation film are formed as different layers at respective pixel regions on a liquid-crystal-side surface of one substrate out of respective substrates which are arranged to face each other in an opposed manner by way of liquid crystal,
at the respective pixel regions, the heights of background layers on which the electrodes which constitute the lower layers with respect to the interlayer insulation films are formed differ with respect to a surface of one substrate, and
the film thickness of the interlayer insulation film is set small with respect to the high background layer out of the respective background layers which differ in height and is set large with respect to the low background layer out of the respective background layers which differ in height.
Means 7.
A liquid crystal display device according to the present invention is, for example, characterized in that:
at respective pixel regions on a liquid-crystal-side surface of one substrate out of respective substrates which are arranged to face each other in an opposed manner by way of liquid crystal,
a pair of electrodes are formed by way of a protective film which is formed by sequentially laminating a first protective film and a second protective film,
the respective electrodes are arranged in a spaced-apart manner in a plan view so as to generate an electric field between the electrodes,
the relationship between the film thicknesses d3, d2 of the first protective film and the second protective film on the electrode arranged as a layer below the protective film and the film thicknesses d3xe2x80x2, d2xe2x80x2 of the first protective film and the second protective film on a region between the pair of electrodes satisfies a following formula (5)
d3xe2x89xa1d3xe2x80x2, d2 less than d2xe2x80x2 less than d2+d4xe2x80x83xe2x80x83(5), and 
the relationship between the layer thickness d1 of liquid crystal on the electrode arranged below the protective film and the layer thickness d1xe2x80x2 of the liquid crystal on the region between the pair of electrodes satisfies a following formula (6).
d1xe2x89xa1d1xe2x80x2 (here, d1xe2x89xa6d1xe2x80x2)xe2x80x83xe2x80x83(6) 
Means 8.
A liquid crystal display device according to the present invention is, for example, characterized in that:
at respective pixel regions formed on a liquid-crystal-side surface of one substrate out of respective substrates which are arranged to face each other in an opposed manner by way of liquid crystal,
a pair of electrodes are formed by way of a protective film which is formed by sequentially laminating a first protective film and a second protective film,
the respective electrodes are arranged in a spaced-apart manner in a plan view so as to generate an electric field between the electrodes, and
in two selected pixel regions, assuming the film thickness of the first protective film in one pixel region as x3, the film thickness of the second protective film in one pixel region as x2, the film thickness of the first protective film in the other pixel region as y3 and the film thickness of the second protective film in the other pixel region as y2, a following formula (7) is established.
x2+x3xe2x89xa1y2+y3, x3 greater than y3, x2 less than y2xe2x80x83xe2x80x83(7) 
Further, when the distance from the substrate to the liquid crystal layer differs, the thickness of the liquid crystal layer differs. In the lateral electric field method, the driving voltage depends on the thickness of the liquid crystal layer. That is, the thicker the liquid crystal layer, the same brightness can be obtained with the lower voltage. On the other hand, this implies that a B-V curve differs between two pixels where the distance from the substrate to the liquid crystal layer differs from each other and hence, the same gray scale cannot be displayed using the equal voltage. Followings are respectively means which can solve such a drawback.
(Means 9)
A liquid crystal display device according to the present invention, for example, comprises;
a liquid crystal layer which is sandwiched between a pair of substrates which face each other in an opposed manner,
a plurality of pixel regions, and
pixel electrodes and counter electrodes which are formed on each pixel region on a liquid-crystal-layer-side surface of one substrate out of the pair of substrates, wherein
each pixel region includes a first pixel and a second pixel respectively having the plurality of counter electrodes formed thereon,
the distance from one substrate to the counter electrodes at the first pixel is set longer than the distance at the second pixel, and
the distance between the plurality of counter electrodes in the pixel at the first pixel is set shorter than the distance at the second pixel.
(Means 10)
A liquid crystal display device according to the present invention, for example, comprises;
a liquid crystal layer which is sandwiched between a pair of substrates which face each other in an opposed manner,
a plurality of pixel regions, and
pixel electrodes and counter electrodes which are formed on each pixel region on a liquid-crystal-layer-side surface of one substrate out of the pair of substrates, wherein
each pixel region includes a first pixel and a second pixel respectively having the plurality of pixel electrodes formed thereon,
the distance from one substrate to the pixel electrodes at the first pixel is set longer than the distance at the second pixel, and
the distance between the plurality of pixel electrodes in the pixel at the first pixel is set shorter than the distance at the second pixel.
(Means 11)
A liquid crystal display device according to the present invention, for example, comprises;
a liquid crystal layer which is sandwiched between a pair of substrates which face each other in an opposed manner,
a plurality of pixel regions, and
pixel electrodes and counter electrodes which are formed on each pixel region on a liquid-crystal-layer-side surface of one substrate out of the pair of substrates, wherein
each pixel region includes a first pixel and a second pixel which differ in the distance from one substrate to the counter electrodes,
the distance from one substrate to the counter electrodes at the first pixel is set longer than the distance at the second pixel, and
the distance between the pixel electrodes and the counter electrodes at the first pixel is set shorter than the distance at the second pixel.
(Means 12)
A liquid crystal display device according to the present invention is, for example, based on the constitution of the means 11, characterized in that the pixel electrodes and the counter electrodes are constituted as separate layers.
(Means 13)
A liquid crystal display device according to the present invention is, for example, based on the constitution of the means 11, characterized in that the pixel electrodes and the counter electrodes are constituted as the same layer.
(Means 14)
A liquid crystal display device according to the present invention is, for example, based on the constitution of the means 9, characterized in that the counter electrodes are formed on an organic film.
(Means 15)
A liquid crystal display device according to the present invention is, for example, based on means 10, characterized in that the pixel electrodes are formed on an organic film.
(Means 16)
A liquid crystal display device according to the present invention is, for example, based on the constitution of the means 13, characterized in that the pixel electrodes and the counter electrodes are formed on an organic film.
(Means 17)
A liquid crystal display device according to the present invention, for example, comprises;
a liquid crystal layer which is sandwiched between a pair of substrates which face each other in an opposed manner,
a plurality of pixel regions, and
pixel electrodes and counter electrodes which are formed on each pixel region on a liquid-crystal-layer-side surface of one substrate out of the pair of substrates, wherein
each pixel region includes a first pixel and a second pixel which differ in the difference between the distance between one substrate and the pixel electrodes and the distance between one substrate and the counter electrodes,
the difference at the first pixel is smaller than the difference at the second pixel,
the distance between one substrate and the pixel electrodes at the first pixel is larger than the distance between one substrate and the pixel electrodes at the second pixel, and
the distance between one substrate and the counter electrodes at the first pixel is larger than the distance between one substrate and the counter electrodes at the second pixel.
(Means 18)
A liquid crystal display device according to the present invention is, for example, based on the constitution of the means 17, characterized in that the pixel electrodes and the counter electrodes are formed as different layers by way of an organic film.
(Means 19)
A liquid crystal display device according to the present invention is, for example, based on the constitution of any one of the means 14 to 16 or 18, characterized in that the organic film is constituted of color filters.
(Means 20)
A liquid crystal display device according to the present invention is, for example, based on the constitution of any one of the means 9 to 11 or 17, characterized in that the first pixel and the second pixel are arranged close to each other.
Further means according to the present invention will become apparent from the description of this specification and attached drawings.